Accelerated communication Electron impact ionization of the TiCl x (x = 1 – 3) free radicals V. Tarnovsky a , R. Basner b , M. Schmidt b , K. Becker a, * a Department of Physics and Engineering Physics, Stevens Institute of Technology, Hoboken, NJ 07030, USA b Institut fu ¨r Niedertemperatur-Plasmaphysik, Friedrich-Ludwig-Jahn-Strasse 19, D-17489 Greifswald, Germany Received 26 March 2001; accepted 7 May 2001 Abstract Titanium tetrachloride (TiCl 4 ) is used for the plasma-assisted chemical vapor deposition of titanium nitride films. We studied the electron impact ionization of TiCl x (x = 1 – 3) free radicals, which are abundant constitutents in TiCl 4 -containing processing plasmas, for electron energies from threshold to 100 eV. Absolute partial cross sections for the formation of all singly charged molecular ions were measured using the fast-beam technique. Dissociative ionization was found to be the dominant process for TiCl 3 whereas the formation of the respective parent ions plays a more important role for TiCl 2 and TiCl. Total single ionization cross sections for the three radicals could not be determined with reasonable accuracy because of problems in the determination of the cross sections for the formation of the atomic ions Ti + and Cl + for the three targets and, as a consequence, no comparison of the measured cross sections with calculated total single ionization cross sections is possible. (Int J Mass Spectrom 208 (2001) 1–5) © 2001 Elsevier Science B.V. Keywords: Titanium tetrachloride; Electron impact ionization; Cross sections; Plasma deposition 1. Introduction Wear and corrosion resistant coatings of TiN can be deposited by plasma-activated chemical vapor deposition at substrate temperatures around 550 °C using low-pressure, nonthermal plasmas with a mix- ture of Ar/H 2 /N 2 /TiCl 4 [1,2]. The plasma chemical processes are determined by the properties of the plasma, which, in turn, depend on the overlap be- tween the electron energy distribution of the plasma electrons and the cross sections for the various elec- tron-initiated processes (e.g. vibrational excitation, dissociative attachment, dissociation, ionization, and dissociative ionization, to name just some of the important electron-driven processes) [3]. The cross sections for the electron interactions with the neutrals in the plasma including the free radicals produced by neutral dissociation of the feed gas molecules are important for a microscopic understanding of the plasma chemical processes and for the modeling of the reactive plasma. Results for the ionization prop- erties of TiCl 4 were reported recently by Basner et al. [4] who carried out a comprehensive study of the * Corresponding author. E-mail: kbecker@stevens-tech.edu 1387-3806/01/$20.00 © 2001 Elsevier Science B.V. All rights reserved PII S1387-3806(01)00464-X International Journal of Mass Spectrometry 208 (2001) 1–5